Several equal spherical planets are in outer space. On the surface of each planet is a set of points which is invisible from any of the remaining planets. Prove that the sum of the areas of all these sets equals the surface area of one planet.
国际数学奥林匹克题 - Spherical Planets
于德利 (2008-06-29 11:26:54) 评论 (0)Several equal spherical planets are in outer space. On the surface of each planet is a set of points which is invisible from any of the remaining planets. Prove that the sum of the areas of all these sets equals the surface area of one planet.